Rate of Growth and Ecesis in Lichens 139 



ditions surrounding them before the 8 years had expired ; I was 

 destroyed by erosion ; I was lost because of poor marking ; others 

 were destroyed through human agency ; in 2 instances there was 

 total lack of succession on chipped-rock surfaces. Of the studies 

 of rate of growth, some of the plants under observation disap- 

 peared through destruction of the substrata on which they were 

 growing, or through various other forms of natural or human 

 interference. In 3 instances the plants ceased to grow soon after 

 they had been marked ; in other 3 instances the logs on which the 

 lichens were growing were destroyed ; in 5 instances the plants 

 began to deteriorate soon after they had been marked, or pos- 

 sibly before the marking was done ; in 4 instances the rocks on 

 which the plants were marked disintegrated rapidly ; and in 3 in- 

 stances the plants appeared healthful for a long period, but failed 

 to grow nevertheless. Though so large a proportion of the 

 studies suffered through various vicissitudes, the 45 reported 

 herein contain data sufficient for our purpose. 



The observations were made in the Ohio area in 7 of the 8 

 years during which the studies ran, omitting a year after the 

 fifth of the series of observations and another after the sixth. 

 The results proved that the added data scarcely justified the 

 labor involved in making observations so frequently. Conse- 

 quently, in the Kentucky area, which was reached by a journey of 

 175 miles, 2 years were allowed to pass without observing after 

 the second series of observations and 3 years after the third series. 

 This gave 7 series of observations for the Ohio area and 4 for 

 the Kentucky area. The dates of observation for the Ohio area 

 are August 4 to 13, 1908; August 1 to 9, 1909 ; July 31 to August 

 5, 1910; July 29 to August 3, 191 1 ; July 31 to August 4, 1912; 

 July 11 to 18, 1914; and September 1 to 7, 1916. The dates for 

 the Kentucky area are October 23 to 30, 1908; August 20 to 27, 

 1909; September 3 to 6, 1912; and August 24 to 26, 1916. Ten 

 of the studies in Ohio were begun in 1909. Only 6 observations 

 were made on these. 



The number of sets of data for each study recorded below 

 corresponds with the number of observations that showed changes 

 worth recording, before the study was destroyed in some manner, 

 before it reached a stage of development after which further 



